Vertebral facet joint prosthesis and method of fixation

ABSTRACT

Devices and methods for altering the spacing and motion at the facet joints of the vertebral column are provided. One embodiment of the invention comprises a prosthesis with surfaces configured to articulate with the facets of the facet joint. A retaining member for anchoring the prosthesis within the facet joint is optionally included. Methods for surgically and less invasively implanting the prosthesis and securing the prosthesis to the articular processes or surrounding soft tissue are also provided.

RELATED APPLICATION INFORMATION

This application is a divisional of U.S. patent application Ser. No.10/865,073, filed Jun. 10, 2004, which claims the priority benefit under35 U.S.C. § 119(e) to a) U.S. Provisional Patent Application No.60/542,351, filed Feb. 6, 2004, b) U.S. Provisional Patent ApplicationNo. 60/542,769, filed Feb. 6, 2004, and c) U.S. Provisional PatentApplication No. 60/542,350, filed Feb. 6, 2004, the disclosures of whichare incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The present invention relates to devices for augmentation andrestoration of vertebral facet joints affected by degeneration and thesurgical method of implanting these devices in the spine.

BACKGROUND OF THE INVENTION

Traumatic, inflammatory, and degenerative disorders of the spine canlead to severe pain and loss of mobility. According to some studies,back and spinal musculoskeletal impairments are the leading causes oflost work productivity in the United States. Pain as a result of sometype of spinal impairment may have its source in a variety ofpathologies or clinical conditions.

One source for back and spine pain is related to degeneration of thefacets of the spine or facet arthritis. Bony contact or grinding ofdegenerated facet joint surfaces may play a role in some pain syndromes.While many technological advances have focused on the spinal disc andartificial replacement or repair of the disc, little advancement infacet repair has been made. Facet joint and disc degeneration frequentlyoccur together. Thus, there is a need to address the clinical concernsraised by degenerative facet joints.

The current standard of care to address the degenerative problems withthe facet joints is to fuse the two adjacent vertebrae together. Byperforming this surgical procedure, the relative motion between the twoadjacent vertebrae is stopped, thus stopping motion of the facets andany potential pain generated as a result thereof. This surgicalprocedure has a high rate of morbidity and can potentially lead tofurther clinical complications such as adjacent segment disorders. Thisprocedure is also not reversible. Therefore, if the patient has anunsatisfactory result, they maybe subject to additional surgical fusionprocedures.

SUMMARY OF THE INVENTION

The present invention aims at addressing the clinical condition of thepatient while allowing the patient to maintain mobility not common withfusion procedures. The device and procedure allow the restoration of therelative spacing between the facets within the facet joint, alleviatingthe bone on bone contact that is common in degenerative facet joints andoften the source of pain generation, while allowing relative motionbetween the facets to continue post-operatively.

While other implants have been proposed with the objective of addressingfacet degeneration by restoring motion, the subject device offers thebenefit of requiring little to no bony resection in order for it to beplaced within the spine. This advantage provides the opportunity for thepatient to rely more on those anatomical structures unaffected bydegeneration while providing for very little morbidity in the surgicalprocedure.

One embodiment of the invention comprises a device for treating spinaldisorders while preserving movement at a facet joint. The devicecomprises a prosthesis having a first face and a second face, where thefirst face is adapted to be secured to the adjacent articular surface ofa facet and the second surface is configured for sliding contact with anadjacent structure. In one embodiment, the device is dimensioned tosubstantially fit within a joint capsule of the facet joint and has athickness generally equal to the normal anatomic spacing between the twofacets of the facet joint. In some embodiments, the device has a curveadapted to match the natural shape of a facet and a size adapted to fitsubstantially within a joint capsule of the facet joint. The device maycomprise at least one material selected from the group consisting ofpolymers, polyetheretherketone (PEEK), polyetherketoneketone (PEKK),polyethylene, fluoropolymers, hydrogels, elastomers, ceramics, zirconia,alumina, silicon nitride; metal(s), titanium, titanium alloy, cobaltchromium, stainless steel, and combinations of these materials. In oneembodiment, the second face of the device comprises a highly polishedsurface. In one embodiment, the first face may comprise a roughenedsurface or a porous surface. In some embodiments, at least one face ofthe device is sufficiently malleable to be capable of generallyconforming to the shape of an adjacent surface or structure under normalanatomical loads.

In one embodiment of the invention, a device for treating spinaldisorders while preserving movement at a facet joint is provided. Thedevice may comprise a prosthesis having a first face and a second face,where the first face is adapted for sliding contact with a firstarticular process of a facet joint and the second surface is configuredfor sliding contact with a second articular process of the facet joint.In one embodiment, the device is dimensioned to substantially fit withina joint capsule of the facet joint and has a thickness generally equalto the normal anatomic spacing between the two facets of a facet joint.In one embodiment, the device has a curve adapted to match the naturalshape of a facet and a size adapted to fit substantially within a jointcapsule of the facet joint. The device has a thickness approximatelyequal to the normal anatomic spacing between the two facets of the facetjoint. In one embodiment, the device has an average thickness within therange of about 0.5 mm to about 3 mm. In one embodiment, the device hasan average thickness within the range of about 1 mm to about 2 mm. Inanother embodiment, the device has a diameter within the range of about5 mm to about 25 mm. In another embodiment, the device has a size withinthe range of about 10 mm to about 20 mm in diameter. In one embodiment,at least one face of the device has a bone contacting surface area ofabout 25 mm² to about 700 mm². In another embodiment, at least one faceof the device has a bone contacting surface area of about 20 mm² toabout 400 mm². In still another embodiment of the device, at least oneface of the device has a bone contacting surface area of about 20 mm² toabout 100 mm². In one embodiment, the device has at least one facecomprising a highly polished surface. In some embodiments, at least oneface of the device is sufficiently malleable to be capable of generallyconforming to the shape of at least a portion of an articular processunder normal anatomical conditions.

The prosthesis may further comprise an anchoring assembly configured togenerally maintain at least a portion of the prosthesis between thefirst articular process and the second articular process of the facetjoint. The anchoring assembly may comprise an elongate member and atleast one retaining member. In one embodiment, the elongate membercomprises a wire or cable. In another embodiment, the elongate membercomprises a solid wire or cable. In still another embodiment, theelongate member comprises a braided cable. The retaining member maycomprise a set screw retaining ring. In one embodiment, at least one endof the device comprises a threaded interface. In one embodiment, theretaining member comprises a threaded retainer. In some embodiments, theretaining member is integrally formed with one end of the elongatemember.

In another embodiment of the invention, the device for treating facetjoint dysfunction is provided. The device comprises a body with a firstface and a second face adapted to contact the bony or cartilaginousarticular surfaces of the facets of adjacent vertebrae. The device hasat least one retaining interface capable of accepting an elongateretainer through it. An elongate retainer is adapted for generallymaintaining the location of the body with respect to the facet joint.The retainer has a first portion adapted to engage a first facet of thefacet joint and a second portion adapted to engage a second facet of thefacet joint. In some embodiments of the invention, the device has agenerally circular cross-section and a diameter adapted to fitsubstantially within a joint capsule of the facet joint. The device hasa thickness generally equal to the normal anatomic spacing between thetwo facets of the facet joint. In still other embodiments of the device,the device has a curve adapted to match the natural shape of the facetand a size adapted to substantially fit within a joint capsule of thefacet. The device may comprise at least one material selected from thegroup consisting of polymers, polyetheretherketone,polyetherketoneketone, polyethylene, fluoropolymers, hydrogels,elastomers, ceramics, zirconia, alumina, silicon nitride; metal(s),titanium, titanium alloy, cobalt chromium, stainless steel, andcombinations of these materials. The elongate retainer may comprise abraided polymer, a braided metal, or a solid structure. In someembodiments of the invention, the elongate retainer comprises aflexibility sufficient to tie a knot in the elongate retainer. Inanother embodiment, at least one end of the elongate retainer has athreaded metal section adapted to accept a threaded knot. A threadedknot is provided to retain the elongate retainer against an articularprocess. In one embodiment of the invention, the threaded section ispressed or crimped onto the elongate retainer. The threaded section andknot may comprise titanium, titanium alloy, cobalt chromium or stainlesssteel. In some embodiments of the invention, the device comprises atleast one face of the highly polished surface. In some embodiments, theelongate member may comprise at least one element with an enlargedcross-sectional area. The elongate member may comprise at least one endof with a bulbous retainer, a flared retainer, a T-bar retainer or anintegral ring retainer. In some embodiments, at least one face of thedevice is sufficiently malleable to be capable of generally conformingto the shape of at least a portion of an articular surface.

In one embodiment of the invention, a prosthesis for treating facetjoint dysfunction is provided. The prosthesis comprises a body with afirst face and a second face, where at least one face adapted forsliding contact with the bony or cartilaginous articular surfaces of thefacets of adjacent vertebrae or the prosthesis has at least oneretaining interface capable of accepting a retainer member. Theretaining member is adapted for securing the location of the body withrespect to at least of the articular surfaces. The retaining member maycomprise a first portion adapted to engage the retaining interface ofthe body and a second portion adapted to engage a first facet of thefacet joint. The retainer may further comprise a third portion adaptedto engage a second facet of the facet joint. In one embodiment, theretainer comprises a threaded shaft and a retaining interface of thebody comprises a threaded hole with an opening on one face of the body.The retaining member may also comprise a projection extending from thebody. In still another embodiment, the retaining member comprises alongitudinal member adapted to engage the retaining interface of thebody and at least one retainer being capable of engaging thelongitudinal member. The retaining ring may comprise a set screwretaining ring. The set screw of the retaining member may have a bluntedtip, curved tip, or piercing tip. Alternatively, at least one of theretaining rings may be a friction fit retaining ring. The body of theprosthesis may be curved. The prosthesis may comprise at least onematerial selected from the group consisting of polymers,polyetheretherketone, polyetherketoneketone, polyethylene,fluoropolymers, hydrogels, elastomers, ceramics, zirconia, alumina,silicon nitride; metal(s), titanium, titanium alloy, cobalt chromium,stainless steel, and combinations of these materials. In someembodiments, at least one face of the prosthesis is sufficientlymalleable to be capable of generally conforming to the shape of at leasta portion of an articular surface.

In one embodiment, a prosthesis for treating facet joint dysfunction isprovided. The prosthesis comprises a first body with a first face and asecond face and a second body within a first face and a second face. Thefirst face of each body is adapted to articulate with the first face ofthe other body and the second face of each body is adapted to engage afacet of a facet joint. The prosthesis may further comprise a retainingmember adapted for securing a location of at least one body. In someembodiments, at least one face of the prosthesis is sufficientlymalleable to be capable of generally conforming to the shape of at leasta portion of an articular surface.

In another embodiment of the invention, a method for treating vertebraldysfunction is provided. This method comprises opening a facet jointcapsule between two facets of adjacent vertebral bodies, distracting theadjacent vertebral bodies from a first spacing to a second spacing andplacing the spacer between the two facets to maintain the secondspacing. The method may further comprise the steps of securing thespacer to one facet of the facet joint. The method may also comprisesecuring the spacer in the facet joint capsule. The step of securing thespacer may comprise drilling a hole through each facet, threading aretainer through the hole of the first facet, threading the retainerthrough the hole in the spacer, threading the retainer through the holeof the second facet, and tying a knot in at least one end of theretainer. The method may further comprise the steps of drilling a holethrough a first facet and a second facet, advancing the retainer throughthe hole of the first facet, advancing the retainer through the hole inthe spacer, threading the retainer through the hole of the second facetand threadably engaging an anchor to at least one end of the retainer.The step of securing the spacer may further comprise providing a spacerwith a retaining member and advancing the retaining member at leastpartially into a facet to engage the facet. The method may also furthercomprise the step of conforming the shape of at least a portion of thespacer to at least a portion of a facet of the facet joint. In a furtherembodiment, the conforming step is performed after the placing step. Inanother embodiment, the conforming step is performed while the spacer isgenerally located between the facets of the facet joint.

In another embodiment of the invention, a method of treating the facetjoint is provided. The method comprises providing a prosthesis dimensionto fit within a facet joint capsule, accessing a facet joint capsulebetween two articular prosthesis of two vertebrae, inserting aprosthesis generally within the joint capsule and maintaining theprosthesis generally between the two articular prosthesis withoutpenetrating the surface of a vertebrae. Maintaining the prosthesis maycomprise anchoring the prosthesis to the joint capsule tissue, orgenerally closing the joint capsule over the prosthesis. The prosthesiscan also be maintained between the articular prosthesis by suturing theprosthesis to the surrounding soft tissue. The method may also furthercomprise the step of conforming the shape of at least a portion of theprosthesis to at least a portion of a facet of the facet joint. In afurther embodiment, the conforming step is performed after the insertingstep. In another embodiment, the conforming step is performed while theprosthesis is generally located between the facets of the facet joint.

BRIEF DESCRIPTION OF THE DRAWINGS

The structure and operation of the invention will be better understoodwith the following detailed description of embodiments of the invention,along with the accompanying illustrations, in which:

FIG. 1 is a lateral elevational view of a portion of the vertebralcolumn;

FIGS. 2A and 2B are schematic superior and side views of an isolatedthoracic vertebra;

FIGS. 3A and 3B are schematic posterior and posterior-obliqueelevational views of a portion of the vertebral column;

FIGS. 4A and 4B are schematic side and superior views of a facet jointin the cervical vertebrae;

FIGS. 5A and 5B are schematic side and superior views of a facet jointin the thoracic vertebrae;

FIGS. 6A and 6B are schematic side and superior views of a facet jointin the lumbar vertebrae;

FIGS. 7A and 7B are schematic views of one embodiment of a facet jointprosthesis comprising a circular disc;

FIG. 8 is a schematic view of the prosthesis from FIG. 7A implanted in afacet joint;

FIGS. 9A and 9B are schematic views of one embodiment of a facet jointprosthesis comprising an octagonal disc;

FIGS. 10A and 10B are schematic views of one embodiment of a facet jointprosthesis comprising a biconcave disc;

FIGS. 11A and 11B are schematic views of one embodiment of a facet jointprosthesis comprising a single-face variable thickness disc;

FIGS. 12A and 12B are schematic views of one embodiment of a facet jointprosthesis comprising a curved disc;

FIG. 13 is a schematic view of the prosthesis from FIG. 12A implanted ina facet joint;

FIGS. 14A and 14B are schematic views of one embodiment of a facet jointprosthesis comprising a disc with a roughened surface on one face;

FIGS. 15A and 15B are schematic views of one embodiment of a facet jointprosthesis comprising a disc with a porous surface on one face;

FIGS. 16A and 16B are schematic views of one embodiment of a facet jointprosthesis comprising a bent disc with a roughened surface on thegreater face;

FIG. 17 is a schematic view of the prosthesis from FIG. 16A implanted ina facet joint;

FIGS. 18A and 18B are schematic views of one embodiment of a facet jointprosthesis comprising two discs, each with a roughened surface on oneface;

FIG. 19 is a schematic view of the prosthesis from FIG. 18A implanted ina facet joint;

FIG. 20 is a schematic view of a retaining member comprising a braidedcable;

FIGS. 21A and 21B are schematic views of one embodiment of a facet jointprosthesis with a retaining interface comprising a centrally locatedhole;

FIGS. 22A and 22B are schematic views of one embodiment of a facet jointprosthesis with a retaining interface comprising an eccentricallylocated hole;

FIGS. 23A and 23B are schematic views of one embodiment of a facet jointprosthesis with a retaining interface comprising an edge contiguoushole;

FIGS. 24A and 24B are schematic views of one embodiment of a facet jointprosthesis comprising two discs, each with an eccentrically locatedhole;

FIGS. 25A and 25B are schematic views of one embodiment of a facet jointprosthesis comprising a curved disc with a retaining interface;

FIG. 26 depicts one embodiment of the invention where the cable isengaged to the articular processes using knots in the cable;

FIGS. 27A and 27B depict another embodiment of the retaining membercomprising a braided cable with threaded ends adapted to accept threadednuts;

FIG. 28 depicts one embodiment of the invention where a cable is engagedto the articular processes using nuts threaded onto the cable;

FIG. 29 depicts a preferred embodiment of the invention comprising acurved prosthesis, cable and two set-screw retaining rings;

FIGS. 30A and 30B are elevational and cross-sectional views of oneembodiment of the set-screw retaining rings, respectively;

FIGS. 31 through 33 are elevational views of various embodiments of thescrew in the set-screw retaining rings;

FIGS. 34A to 35B are one embodiment of the invention comprising frictionfit retaining rings. FIGS. 34A and 34B depict the retaining rings intheir reduced state and FIGS. 35A and 35B depict the retaining rings intheir expanded state;

FIGS. 36A to 36C illustrate embodiments of the invention comprising aprosthesis with a close-ended threaded retaining interface and athreaded retaining member;

FIGS. 36B and 36C depict a threaded retaining member with a pivotablewasher;

FIG. 37A is a cross sectional view of the prosthesis in FIG. 36Aimplanted in a facet joint; FIG. 37B is a cross sectional view of theprosthesis in FIG. 36B implanted in a facet joint;

FIG. 38 is a cross sectional view of a two-part prosthesis comprisingflat discs implanted into a facet joint;

FIG. 39 is a cross sectional view of a two-part prosthesis comprisingcurved discs implanted into a facet joint;

FIGS. 40A and 40B are schematic views of one embodiment of a facet jointprosthesis with an integral retaining member comprising a centrallylocated barbed spike;

FIGS. 41A and 41B are schematic views of one embodiment of a facet jointprosthesis with an integral retaining member comprising an eccentricallylocated barbed spike;

FIG. 42 depicts the prosthesis of FIG. 38A implanted into a facet joint;

FIG. 43 illustrates a two-part prosthesis implanted into a facet joint;

FIG. 44 shows one embodiment of the invention comprising a prosthesiswith multiple anchoring projections;

FIG. 45 shows the prosthesis of FIG. 44 implanted into a facet joint;

FIGS. 46A and 46B depict one embodiment of the invention comprising aprosthesis with a rigid soft tissue side anchor;

FIGS. 47A and 47B depict one embodiment of the invention comprising aprosthesis with an embedded flexible soft tissue side anchor;

FIG. 48 depicts one embodiment of the invention depicting a posteriorsurgical approach for implanting a prosthesis in the cervical vertebrae;

FIG. 49 depicts one embodiment of the invention depicting thecross-sectional surgical approach for implanting a prosthesis in thecervical vertebrae;

FIG. 50 depicts one embodiment of the invention depicting a posteriorsurgical approach for implanting a prosthesis in the thoracic vertebrae;and

FIGS. 51A to 51E depicts one embodiment of the invention depicting aposterior surgical approach for implanting a prosthesis in the lumbarvertebrae; FIGS. 51A to 51C are posterior views of the surgicalprocedure and FIGS. 51D and 51E are cross sectional views of thesurgical procedure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A. Anatomy of the Spine

As shown in FIG. 1, the vertebral column 2 comprises a series ofalternating vertebrae 4 and fibrous discs 6 that provide axial supportand movement to the upper portions of the body. The vertebral column 2typically comprises thirty-three vertebrae 4, with seven cervical(C1-C7), twelve thoracic (T1-T12), five lumbar (L1-15), five fusedsacral (S1-S5) and four fused coccygeal vertebrae. FIGS. 2A and 2Bdepict a typical thoracic vertebra. Each vertebra includes an anteriorbody 8 with a posterior arch 10. The posterior arch 10 comprises twopedicles 12 and two laminae 14 that join posteriorly to form a spinousprocess 16. Projecting from each side of the posterior arch 10 is atransverse 18, superior 20 and inferior articular process 22. The facets24, 26 of the superior 20 and inferior articular processes 22 form facetjoints 28 with the articular processes of the adjacent vertebrae. SeeFIGS. 3A and 3B. The facet joints are true synovial joints withcartilaginous surfaces and a joint capsule.

The orientation of the facet joints vary, depending on the level of thevertebral column. In the C1 and C2 vertebrae, the facet joints areparallel to the transverse plane. FIGS. 4A to 6B depict the orientationsof the facet joints at different levels of the vertebral column. In theC3 to C7 vertebrae shown in FIGS. 4A and 4B, the facets are oriented ata 45-degree angle to the transverse plane 30 and parallel to the frontalplane 32, respectively. This orientation allows the facet joints of thecervical vertebrae to flex, extend, lateral flex and rotate. At a45-degree angle in the transverse plane 30, the facet joints of thecervical spine can guide, but do not limit, the movement of the cervicalvertebrae. FIGS. 5A and 5B depict the thoracic vertebrae, where thefacets are oriented at a 60-degree angle to the transverse plane 30 anda 20-degree angle to the frontal plane 32, respectively. Thisorientation is capable of providing lateral flexion and rotation, butonly limited flexion and extension. FIGS. 6A and 6B illustrate thelumbar region, where the facet joints are oriented at 90-degree anglesto the transverse plane 30 and a 45-degree angle to the frontal plane32, respectively. The lumbar vertebrae are capable of flexion, extensionand lateral flexion, but little, if any, rotation because of the90-degree orientation of the facet joints in the transverse plane. Theactual range of motion along the vertebral column can vary considerablywith each individual vertebra.

In addition to guiding movement of the vertebrae, the facet joints alsocontribute to the load-bearing ability of the vertebral column. Onestudy by King et al. Mechanism of Spinal Injury Due to CaudocephaladAcceleration, Orthop. Clin. North Am., 6:19 1975, found facet jointload-bearing as high as 30% in some positions of the vertebral column.The facet joints may also play a role in resisting shear stressesbetween the vertebrae. Over time, these forces acting on the facetjoints can cause degeneration and arthritis.

B. Joint Prosthesis

In one embodiment of the invention, a device for restoring the spacingbetween two facets of a facet joint is provided. As shown in FIGS. 7Aand 7B, the device comprises a prosthesis 34 with a least two faces, afirst face 36 adapted to contact the articular surface of one facet ofthe facet joint and a second face 38 adapted to contact the articularsurface of the other facet. In one embodiment, the prosthesis 34 has agenerally circular profile and is sized to fit generally within thejoint capsule of the facet joint 28. FIG. 8 illustrates the prosthesis34 of FIGS. 7A and 7B positioned in a facet joint. In other embodimentof the invention, the prosthesis can have any of a variety of profiles,including but not limited to square, rectangle, oval, star, polygon orcombination thereof. An octagonal prosthesis is shown in FIGS. 9A and9B. In one embodiment of the invention, a prosthesis having the desiredshape is selected from an array of prostheses after radiographicvisualization of the articular processes and/or by radio-contractinjection into the facet joint to visualize the joint capsule. In oneembodiment, the prosthesis has a diameter of about 4 mm to about 30 mm.In another embodiment, the prosthesis has a diameter of about 5 mm toabout 25 mm. In still another embodiment, the prosthesis has a diameterof about 10 mm to about 20 mm. In one embodiment, the prosthesis has across-sectional area of about 10 mm² to about 700 mm². In anotherembodiment, the prosthesis has a cross-sectional area of about 25 mm² toabout 500 mm². In still another embodiment, the prosthesis has across-sectional area of about 20 mm² to about 400 mm², and preferablyabout 25 mm² to about 100 mm².

The prosthesis has a thickness generally equal to about the anatomicspacing between two facets of a facet joint. The prosthesis generallyhas a thickness within the range of about 0.5 mm to about 3.0 mm. Incertain embodiments, the prosthesis has a thickness of about 1 mm toabout 2 mm. In one preferred embodiment, the prosthesis has a thicknessof about 0.5 mm to about 1.5 mm. In one embodiment, the thickness of theprosthesis is nonuniform within the same prosthesis. For example, inFIGS. 10A and 10B, the thickness of the prosthesis 42 is increasedaround the entire outer edge 44, along at least one and, as illustrated,both faces 46, 48. In FIGS. 11A and 11B, only a portion of the edge 44on one face 46 of the prosthesis 42 has a thickness that is greater thanthe thickness of a central region, and, optionally, also thicker thanthe typical anatomic spacing between two facets of a facet joint. Anincreased edge thickness may resist lateral displacement of theprosthesis out of the facet joint.

In some embodiments of the invention, the prosthesis is configured toprovide an improved fit with the articular process and/or joint capsule.For example, in FIGS. 12A and 12B, the prosthesis 49 has a bend, angleor curve 50 to generally match the natural shape of an articular facet.FIG. 13 depicts the prosthesis of FIGS. 12A and 12B positioned in afacet joint. The prosthesis may be rigid with a preformed bend.Alternatively, the prosthesis may be sufficiently malleable that it willconform post implantation to the unique configuration of the adjacentfacet face. Certain embodiments of the invention, such as those depictedin FIG. 8 and FIG. 13, the prosthesis is configured to be implantedbetween the articular processes and/or within the joint capsule of thefacet joint, without securing of the prosthesis to any bony structures.Such embodiments can thus be used without invasion or disruption of thevertebral bone and/or structure, thereby maintaining the integrity ofthe vertebral bone and/or structure.

In one embodiment, at least a portion of one surface of the prosthesisis highly polished. A highly polished portion of the prosthesis mayreduce the surface friction and/or wear in that portion of theprosthesis as it contacts bone, cartilage or another surface of theprosthesis. A highly polished surface on the prosthesis may alsodecrease the risk of the prosthesis wedging between the articularsurfaces of the facet joint, which can cause pain and locking of thefacet joint.

In one embodiment, shown in FIGS. 14A and 14B, at least a portion of onesurface of the prosthesis 50 has a roughened surface 52. A roughenedsurface may be advantageous when in contact with a bone or tissuesurface because it may prevent slippage of the prosthesis 50 against thebone and aid in maintaining the prosthesis 50 in the joint. In oneembodiment of the invention, shown in FIGS. 15A and 15B, at least aportion of one surface of the prosthesis 50 has a porous surface 54. Aporous surface 54 can be created in any a variety of ways known in theart, such as by applying sintered beads or spraying plasma onto theprosthesis surface. A porous surface 54 can allow bone to grow into orattach to the surface of the prosthesis 50, thus securing the prosthesis50 to the bone. In one embodiment, an adhesive or sealant, such as acyanoacrylate, polymethylmethacrylate, or other adhesive known in theart, is used to bond one face of the prosthesis to an articular surface.

In one embodiment of the invention, one surface of the prosthesis isroughened or porous and a second surface that is highly polished. Thefirst surface contacts or engages one facet of the facet joint and aidsin maintaining the prosthesis between the articular surfaces. The secondsurface of the prosthesis is highly polished and contacts the otherfacet of the facet joint to provide movement at that facet joint. FIGS.16A and 16B represent one embodiment of the prosthesis comprising acurved or bent disc 56 with a roughened surface 52 on the greater face58 of the disc and a highly polished surface 60 on the lesser face 62.FIG. 17 depicts the prosthesis of FIGS. 16A and 16B positioned in afacet joint. The prosthesis generally maintains a fixed positionrelative to the facet contacting the roughened surface while themovement of the facet joint is preserved between the other facet and thehighly polished lesser face of the prosthesis.

FIGS. 18A and 18B show one embodiment of the invention, where theprosthesis 64 comprises two separate discs 66, each disc comprising afirst face 68 that articulates with the complementary first face 68 ofthe other disc, and a second face 70 adapted to secure the disc to theadjacent bone or cartilage of one facet of the facet joint 28. In oneembodiment of the invention, the thickness of one disc will generally beabout half of the anatomic spacing between two facets of the facetjoint. In other embodiments of the invention, the prosthesis comprisesthree or more discs. In one embodiment the total thickness of all thediscs is generally about 25% to about 300% of the anatomic spacingbetween the two facets. In another embodiment, the total thickness ofthe discs is generally about 50% to about 150% of the anatomic spacing.In still another embodiment, the total thickness of the discs is about75% to about 125% of the anatomic spacing. Each disc of the two-partprosthesis can otherwise also have features similar to those of asingle-disc prosthesis, including but not limited to curved or bentconfigurations, highly polished or roughened surfaces, and other featurementioned below. The two discs need not have the same size, thickness,configuration or features. FIG. 19 depicts one embodiment of a two-partprosthesis 64 positioned within a facet joint 28.

The prosthesis can be manufactured from any of a variety of materialsknown in the art, including but not limited to a polymer such aspolyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyethylene,fluoropolymer, hydrogel, or elastomer; a ceramic such as zirconia,alumina, or silicon nitride; a metal such as titanium, titanium alloy,cobalt chromium or stainless steel; or any combination of the abovematerials.

C. Prosthesis with a Retaining Configuration

In one embodiment of the invention, the prosthesis is maintained betweenthe two facets of the facet joint by taking advantage of the jointcapsule and/or other body tissue surrounding the facet joint to limitthe migration of the prosthesis out of the facet joint. In someembodiments of the invention, the shape of the prosthesis itself iscapable of resisting displacement of the prosthesis from its positiongenerally between the facet joint surfaces. In one embodiment, a concaveor biconcave configuration resists displacement of the prosthesis byproviding an increased thickness at the periphery of the prosthesis thatrequires a larger force and/or greater distraction of facet jointsurfaces in order to cause displacement. In other embodiments, surfacetreatments or texturing are used to maintain the prosthesis against afacet of the facet joint, as described previously. In some embodiments,a combination of disc configuration, surface texturing and existing bodytissue or structures are used to maintain the position of theprosthesis.

Bone growth facilitators, electrical current, or other known techniquesmay be used to accelerate osteoincorporation of textured or microporousanchoring surfaces.

D. Prosthesis with a Retaining Member

The prosthesis may be configured with a retaining interface to engage aretaining member that facilitates retention of the prosthesis within thejoint capsule of the facet joint. Use of a retaining member may beadvantageous for preventing migration of the prosthesis over time use orwith the extreme ranges of vertebral movement that may distract thearticular surfaces sufficiently to allow the prosthesis to slip out.

1. Wire/Cable Retaining Member

In one embodiment of the invention, shown in FIGS. 20 to 21B, theretaining member comprises a wire or cable 72 with a portion 74 thatengages the prosthesis 76 at a retaining interface 78, and at least oneother portion 80 that engages or anchors to the bone or soft tissuesurrounding the facet joint. The wire or cable may be solid, braided ormulti-filamented. The retaining member in this embodiment will bedescribed primarily as a cable or wire, but it is to be understood thatany of a variety of elongate structures capable of extending through acentral aperture will also work, including pins, screws, and singlestrand or multistrand polymeric strings or weaves, polymeric meshes andfabric and other structures that will be apparent to those of skill inthe art in view of the disclosure herein.

The cross-sectional shape of the retaining member can be any of avariety of shapes, including but not limited to circles, ovals, squares,rectangles, other polygons or any other shape. The wire or cablegenerally has a diameter of about 0.5 mm to about 2 mm and a length ofabout 5 mm to about 60 mm. In another embodiment, wire or cable has adiameter of about 0.25 mm to about 1 mm, and preferably about 0.75 mm toabout 1.25 mm. The diameter of the wire or cable may vary along thelength of the wire or cable. In one embodiment, the wire or cable has alength of about 10 mm to about 40 mm. In another embodiment, the wire orcable has a length of about 20 mm to about 30 mm.

In one embodiment, shown in FIGS. 21A and 21B, the retaining interface78 of the prosthesis 76 is a conduit between the two faces 82, 84 of theprosthesis 76, forming an aperture 78. In one embodiment, the aperture78 has a diameter larger than the diameter of the wire or cable 72, toprovide the prosthesis 76 with a range of motion as the facet jointmoves. The aperture 78 inside diameter may be at least about 110%, oftenat least about 150% and in certain embodiments at least about 200% or300% or greater of the outside diameter or corresponding dimension ofthe retaining member in the vicinity of the engagement portion 78. Thecross-sectional shape of the aperture 78 can match or not match thecross sectional shape of the wire or cable used.

In another embodiment, the retaining interface 78 extends only partiallythrough the prosthesis 72. The retaining interface 78 may be locatedgenerally in the center of the prosthesis, or it may be locatedeccentrically, as depicted in FIGS. 22A and 22B. In one embodiment,shown in FIGS. 23A and 23B, the retaining interface 78 is located at theedge 86 of the prosthesis 76 such that the interior surface of the hole78 is contiguous with the outer edge of the prosthesis. Thisconfiguration of the retaining interface 78 does not require the cable72 to be threaded through the retaining interface 78 and may facilitateengagement of the retaining member with the prosthesis. FIGS. 24A and24B depict an embodiment of the invention comprising a two-partprosthesis 88. Either a single cable or two separate cables may be usedretain both discs within the facet joint. FIGS. 25A and 25B depictanother embodiment of the invention comprising a curved prosthesis 90with a retaining interface 78 adapted to accept a cable.

In FIG. 26, the wire or cable 72 is secured to the articular processes20, 22 by tying one or more knots 92 in the cable 72 that can resistpulling of the wire or cable through the articular process. In anotherembodiment, one or both ends of the wire or cable are provided with ananchor to resist migration of the implants. As shown in FIGS. 27A and27B, one or both ends of the wire or cable 72 may be threaded such thata nut 94 can be tightened on the wire or cable 72 to secure the wire orcable to the articular processes 20, 22. FIG. 28 depicts the attachmentof a nut onto a threaded end of a cable. The threaded portion 96 of thewire or cable can be secured to the cable by pressing, crimping ortwisting the threaded 96 portion onto the cable 72. In one embodiment,the threaded portion 96 is made from titanium, titanium alloy, cobaltchromium, stainless steel, or any combination thereof.

In one embodiment, the wire or cable has two threaded ends 96 forengaging the bony or cartilaginous tissue, one portion for each facet ofthe facet joint.

In another embodiment, shown in FIG. 29, the wire or cable is secured tothe articular process with retaining rings 98. As depicted in FIGS. 30Aand 30B, the retaining rings 98 comprise a ring 100 with a central lumen102 and a locking element to facilitate locking the ring 100 to aretaining member. The central lumen 102 is adapted to accept insertionof a wire or cable through it. The illustrated locking element is in theform of a side lumen 104 which is threaded and configured to accept arotatable screw 106 with a proximal end 108, a threaded body 110 and adistal end 112. The threaded body 110 is complementary to the threads ofthe side lumen 104 so that when the screw 106 is rotated at its distalend 112, the proximal end 108 of the screw 106 moves further into thecentral lumen 102 and is capable of applying increasing force to a wireor cable inserted through the central lumen 102. In one embodiment, theforce on the wire or cable is capable of creating a friction fit or amechanical interfit to resist movement between the wire or cable and theretaining ring 98, thereby securing the wire or cable to the articularprocess 20 or 22. As shown in FIGS. 31 to 33, the distal end 112 of thescrew 106 can be configured to engage the wire or cable in any of avariety designs, including but no limited to a blunt tip 114, curved tip116 and piercing tip 118.

In another embodiment, depicted in FIGS. 34A and 34B, the wire or cableis securable to the articular process with a retaining ring 120 haveradially inward biased projections 122 defining a central lumen 124. Thecentral lumen has a cross-sectional shape smaller than that of the wireor cable but is capable of enlargement when the inward projections 122are bent away, as shown in FIGS. 35A and 35B. The inward projections 122apply increasing force to the wire or cable within the central lumen 124as the projections 122 are bent, thereby creating a friction fit.

In one embodiment of the invention, one end of the wire or cableretaining member is preformed with a retainer for engaging the articularprocess. The retainer may be a preformed ring, bulb, flared end, T-barend, or any of a variety of shapes having a greater cross sectional areathan the other portions of the wire or cable retaining member. Thisconfiguration of the wire or cable retaining member is adapted to engagean articular process by passing the free end of a wire or cableretaining member through an articular process such that the end with thepreformed retainer can engage the articular process.

In one embodiment, the wire or cable retaining member is secured to thearticular processes with sufficient laxity or length between the securedends or between the prosthesis and one secured end so that the twoarticular processes are not fixed in position relative to each other andremain capable of performing movements such as flexion, extension,lateral flexion and/or rotation. In one embodiment, the retaining membercomprises a cable of braided polymer, including but not limited to abraided polymer such as PEEK or PEKK, or a braided metal, such asbraided cobalt chromium or titanium. The cable can be selected withdifferent degrees of flexibility to provide different degrees ofmovement at that facet joint. The cable has a first segment capable ofengaging the prosthesis at its retaining interface to limit the movement

2. Screw/Bolt Retaining Member

In one embodiment of the invention, shown in FIG. 36A, the retainingmember comprises a screw or bolt 126 with a proximal end 128, body 130and distal end 132. The distal end 132 of the screw or bolt is capableof forming a mechanical interfit with a complementary retaininginterface 134 on the prosthesis or spacer 136. The distal end 132typically comprises threads, but one skilled in the art will understandthat other configurations may be used to form a mechanical interfit. Thecomplementary retaining interface 134 on the prosthesis 136 could be athreaded through hole or preferably, a close-ended hole. The proximalend 128 of the screw or bolt 126 has a hex or other type of interfaceknown in the art, capable of engaging a rotating tool to manipulate thescrew or bolt 126. The body of the screw or bolt 126 has a lengthsufficient to at least span the length of the hole or conduit createdthrough the articular process for securing the prosthesis. In FIG. 36B,the retaining member further comprises a pivotable washer 127 with apivot surface 129 that articulates with the proximal end 128 of thescrew 126. In one embodiment, the pivotable washer 127 is capable of arange of positions relative to the screw 126 and provides the screw 126with a better surface area contact with the bone.

FIG. 37 is a cross-sectional view of a facet joint 28 with a spacer 136bolted to one articular process 20 of a facet joint 28. The spacer 136position is fixed relative to one facet 24 of the joint 28, but providesfor spacing and movement of the other facet 26 with respect to thespacer 136. In embodiments of the invention comprising a two-partprosthesis, shown in FIGS. 38 and 39, each disc may have its own screwor bolt retaining member. FIG. 38 depicts a flat two-part prosthesis 138and FIG. 39 depicts a curved two-part prosthesis 140.

3. Projection Retaining Member

In some embodiments of the invention, shown in FIGS. 40A through 41B,the retaining member is integral with or attached to the prosthesis andcomprises a projection 142 from the prosthesis 144 that is adapted toengage the adjacent articular process or surrounding tissue. In oneembodiment, the projection comprises at least one spike 142 or hookprojecting from one face of the prosthesis 144. In one embodiment, thespike 142 or hook can be ribbed, barbed or threaded to resist separationafter insertion into bone or tissue. FIG. 42 depicts the prosthesis 144of FIG. 40A engaged to a facet 24 of the facet joint 28. In oneembodiment comprising a two-part prosthesis 146, shown in FIG. 43, eachdisc 148 may have its own projection-retaining member 142. In someembodiments of the invention, as depicted in FIG. 44, more than oneprojection 150 is provided on the prosthesis 152. FIG. 45 illustratesthe prosthesis of FIG. 44 placed in a facet joint 28. The projections150 may be angled with respect to the prosthesis 152 to resistdislodgement by the movement at the joint.

FIGS. 46A to 47B illustrate embodiments of the invention where theretaining member comprises a projection 154 extending laterally such asfrom the side of the prosthesis 156, and adapted to engage the softtissue surrounding the facet joint, rather than a bony or cartilaginousarticular process. In one example, the prosthesis of FIG. 46 could beinserted into a facet joint through an incision made in the jointcapsule, but the integrity of the joint capsule opposite the incisionsite is maintained and used as an anchoring site for the prosthesis. Theorientation of the projection can be fixed as in FIG. 44, or flexible.FIG. 47 depicts a flexible tether such as a wire 158 with its proximalend 160 embedded in or otherwise attached to the prosthesis and one ormore barbs which may be attached to its distal end 162. A flexibleprojection may provide greater selection of soft tissue anchoring sitesfor the prosthesis.

In one embodiment of the invention, the joint capsule is closed afterplacement of the prosthesis. Closure may be performed using adhesives,suturing, stapling or any of a variety of closure mechanisms known inthe art.

E. Accessing the Facet Joints

1. Surgical Approach to the Cervical Spine

In one embodiment of the invention, general anesthesia is achieved andthe patient is positioned prone on a turning frame or three-point headrest attached to the table. Skeletal traction is performed using tongs.The patient is prepped and draped in the usual sterile fashion.Pre-operative radiographic films are reviewed and any vertebralanomalies or variations are noted. In one embodiment, the spinousprocesses are palpated to identify the location of the cervicalvertebrae and a skin incision is made over the desired vertebrae, asshown in FIG. 48. In another embodiment, a paraspinous skin incision ismade over the desired facet joint. The exposed skin edges andsubcutaneous tissue are injected with epinephrine 1:500,000 solution tofacilitate hemostasis. Dissection to the spinous processor facet jointis performed using an electrocautery knife. In one embodiment, shown inFIG. 49, dissection is performed along the nuchal ligament 164 to avoidcutting into vascular muscle tissue. Soft tissue retractors are used tomaintain tissue tension and aid the dissection process. The ligamentousattachments to the spinous process 16 are detached and the facet jointsare exposed. In another embodiment, dissection is performed through themuscle tissue to directly access the facet joint. The joint capsule ofthe facet joint is opened by incision or piercing. The facets of thefacet joint are distracted as required to provide access to the jointspace. In one embodiment, the affected facet joint is sized and a jointprosthesis is selected. In one embodiment, the articular process orprocesses are prepared for receiving the joint prosthesis, including butnot limited to roughening the articular surface of the articular processand/or drilling a hole for the prosthesis anchor or retaining member.The prosthesis is inserted into the facet joint space and the anchor orretaining member, if any is attached to the articular process. The stepsare repeated until all the joint prostheses have been inserted. Thesurgical site is closed in layers with a suction tube or drainage tubein place. The surgical site is cleaned and dressed.

2. Surgical Approach to the Thoracic Spine

In one embodiment of the invention, general anesthesia is achieved andthe patient is positioned prone on a padded spinal operating frame. Thepatient is prepped and draped in the usual sterile fashion.Pre-operative radiographic films are reviewed and any vertebralanomalies or variations are noted. In one embodiment, shown in FIG. 50,a midline skin incision is made over the desired vertebrae. In anotherembodiment, a paraspinous skin incision is made over the desired facetjoint. The exposed skin edges, subcutaneous tissue and erector spinaemuscles are injected with epinephrine 1:500,000 solution to facilitatehemostasis. Dissection is performed using an electrocautery knife orscalpel through the superficial and lumbodorsal fascia to the tips ofthe spinous processes. The erector spinae muscle is reflected laterallyto the tips of the transverse processes, thereby exposing the posteriorarch. After exposure of all the desired vertebrae is achieved, anintra-operative x-ray is obtained to confirm access to the desiredvertebrae. The facets of the facet joint are distracted as required toprovide access to the joint space. The joint capsule of the facet jointis opened by incision or piercing. In one embodiment, the affected facetjoint is sized and a joint prosthesis is selected. In one embodiment,the articular process or processes are prepared for receiving the jointprosthesis, including but not limited to roughening the articularsurface of the articular process and/or drilling a hole for theprosthesis anchor or retaining member. The prosthesis is inserted intothe facet joint space and the anchor or retaining member, if any isattached to the articular process. The steps are repeated until all thejoint prostheses have been inserted. The surgical site is closed inlayers with a suction tube or drainage tube in place. The surgical siteis cleaned and dressed.

3. Surgical Approach to the Lumbar Spine

In one embodiment of the invention, general anesthesia is achieved andthe patient is positioned prone or kneeling on a padded spinal operatingframe. In one embodiment, by allowing the abdomen to hang free,intravenous pressure is reduced and blood loss during the procedure isdecreased. The patient is prepped and draped in the usual sterilefashion. Pre-operative radiographic films are reviewed and any vertebralanomalies or variations are noted. FIG. 51A illustrates a midline skinincision is made over the desired vertebrae. The exposed skin edges andsubcutaneous tissue are injected with epinephrine 1:500,000 solution tofacilitate hemostasis. In FIGS. 51B and 51C, dissection is continued tothe lumbodorsal fascia and the surgical site is exposed by retractingthe skin and subcutaneous tissue laterally. In FIGS. 51D and 51E, bluntfinger dissection is used between the multifidus and longissimus musclesto access the facet joints. Self-retaining Gelpi retractors are insertedbetween the muscle groups. Electrocautery or elevators are used toseparate the transverse fibers of the multifidus from their heavyfascial attachments. Exposure of the transverse processes and fascialplanes is continued. Cautery may be used to provide hemostasis from thelumbar arteries and veins along the base of the transverse processes.The facets of the facet joint are distracted as required to provideaccess to the joint space. The joint capsule of the facet joint isopened by incision or piercing. In one embodiment, the affected facetjoint is sized and a joint prosthesis is selected. In one embodiment,the articular process or processes are prepared for receiving the jointprosthesis, including but not limited to roughening the articularsurface of the articular process and/or drilling a hole for theprosthesis anchor or retaining member. The prosthesis is inserted intothe facet joint and the anchor or retaining member, if any is attachedto the articular process. The steps are repeated until all the jointprostheses have been inserted. The surgical site is closed in layersover a suction tube and the skin flaps are sutured down to the fascia toeliminate any dead space in the tissue. The surgical site is cleaned anddressed.

4. Minimally Invasive Approach to the Cervical Spine

In one embodiment of the invention, general or local anesthesia isachieved and the patient is positioned prone on a turning frame orthree-point head rest attached to the table. Skeletal traction isperformed using tongs. The patient is prepped and draped in the usualsterile fashion. Pre-operative radiographic films are reviewed and anyvertebral anomalies or variations are noted. The spinous processes arepalpated to identify the location of the cervical vertebrae and a small1 cm skin incision is made over the desired insertion site. Hemostasisis achieved with infiltration of epinephrine 1:500,000 solution aroundthe incision site. Under fluoroscopy, a trocar or needle is insertedthrough the incision site and joint capsule to the desired facet joint.The needle or trocar is replaced with an introducer. In one embodiment,insertion is performed along the nuchal ligament to avoid cutting intovascular muscle tissue. In another embodiment, insertion is performeddirectly through the skin and muscle overlying the facet joint. Thefacets of the facet joint are distracted as required to provide accessto the joint space. In one embodiment, the affected facet joint is sizedby injecting a radio-contrast agent into the facet joint and a jointprosthesis is selected. In one embodiment, the articular process orprocesses are prepared for receiving the joint prosthesis, including butnot limited to roughening the articular surface of the articular processand/or drilling a hole using endoscopic instruments known in the art.The prosthesis is inserted into the facet joint space through theintroducer and an anchor or retaining member, if any is attached to thearticular process. The steps are repeated until all the joint prostheseshave been inserted. The surgical site is closed, cleaned and dressed.

5. Minimally Invasive Approach to the Thoracic Spine

In one embodiment of the invention, general or local anesthesia isachieved and the patient is positioned prone on a padded spinaloperating frame. The patient is prepped and draped in the usual sterilefashion. Pre-operative radiographic films are reviewed and any vertebralanomalies or variations are noted. A small 1 cm skin incision is madeover the desired insertion site. Hemostasis is achieved by injectingepinephrine 1:500,000 solution around the incision site. Underfluoroscopy, a trocar or needle is inserted through the superficial andlumbodorsal fascia, the erector spinae muscle and joint capsule toaccess the facet joint. The trocar or needle is replaced with anintroducer. The facets of the facet joint are distracted as required toprovide access to the joint space. An intra-operative x-ray orfluoroscopy is obtained to confirm access to the desired facet joint. Inone embodiment, the affected facet joint is sized and a joint prosthesisis selected. In one embodiment, the articular process or processes areprepared for receiving the joint prosthesis, including but not limitedto roughening the articular surface of the articular process and/ordrilling a hole for the prosthesis anchor or retaining member, usingendoscopic instruments known in the art. The prosthesis is inserted intothe facet joint space and the anchor or retaining member, if any isattached to the articular process. The steps are repeated until all thejoint prostheses have been inserted. The surgical site is closed,cleaned and dressed.

6. Minimally Invasive Approach to the Lumbar Spine

In one embodiment of the invention, general or local anesthesia isachieved and the patient is positioned prone or kneeling on a paddedspinal operating frame. In one embodiment, by allowing the abdomen tohang free, intravenous pressure is reduced and blood loss during theprocedure is decreased. The patient is prepped and draped in the usualsterile fashion. Pre-operative radiographic films are reviewed and anyvertebral anomalies or variations are noted. A small 1 cm skin incisionis made over the desired insertion site. Hemostasis is achieved byinjecting epinephrine 1:500,000 solution around the incision site. Underfluoroscopy, a trocar or needle is inserted through the lumbodorsalfascia. The trocar or needle is replaced with an introducer. In oneembodiment, radio-contrast agent is injected through the introducer toidentify the junction between the lumbodorsal fascia and the multifidusand longissimus muscles. A blunt dissector is inserted through theintroducer to dissect between the multifidus and longissimus muscles andpierce the joint capsule to access the facet joints. The facets of thefacet joint are distracted as required to provide access to the jointspace. In one embodiment, the affected facet joint is sized and a jointprosthesis is selected. In one embodiment, the articular process orprocesses are prepared for receiving the joint prosthesis, including butnot limited to roughening the articular surface of the articular processand/or drilling a hole for the prosthesis anchor or retaining member.The prosthesis is inserted into the facet joint space and the anchor orretaining member, if any is attached to the articular process. The stepsare repeated until all the joint prostheses have been inserted. Thesurgical site is closed, cleaned and dressed.

While embodiments of this invention have been particularly shown anddescribed with references to embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the scope of the invention. Forall of the embodiments described above, the steps of the methods neednot be performed sequentially.

1. A method of treating vertebral dysfunction, comprising: opening afacet joint capsule between two facets of adjacent vertebral bodies;distracting the adjacent vertebral bodies from a first spacing to asecond spacing; and placing a spacer between the two facets to maintainthe second spacing.
 2. The method of claim 1, further comprising thesteps of: securing the spacer to one facet of the facet joint.
 3. Themethod of claim 1, further comprising the steps of: securing the spacerin the facet joint capsule.
 4. The method of claim 3, wherein the stepof securing the spacer comprises: drilling a hole through each facet;threading a retainer through the hole of the first facet; threading theretainer through the hole in the spacer; threading the retainer throughthe hole of the second facet; and tying a knot in at least one end ofthe retainer.
 5. The method of claim 3, further comprising the steps of:drilling a hole through a first facet and a second facet; advancing aretainer through the hole of the first facet; advancing the retainerthrough the hole in the spacer; threading the retainer through the holeof the second facet; and threadably engaging an anchor to at least oneend of the retainer.
 6. The method of claim 3, further wherein the stepof securing the spacer comprises: providing a spacer with a retainingmember; and advancing the retaining member at least partially into afacet to engage the facet.
 7. The method of claim 1, further comprisingthe step of: conforming the shape of at least a portion of the spacer toat least a portion of a facet of the facet joint.
 8. The method of claim7, wherein the conforming step is performed after the placing step. 9.The method of claim 7, wherein the conforming step is performed whilethe spacer is generally located between the facets of the facet joint.10. A method of treating a facet joint, comprising the steps of:providing a prosthesis dimensioned to fit within a facet joint capsule;accessing a facet joint capsule between two articular processes of twovertebrae; inserting a prosthesis generally within the joint capsule;and maintaining the prosthesis generally between the two articularprocesses without penetrating the surface of a vertebrae.
 11. The methodof claim 10, wherein the maintaining step comprises anchoring theprosthesis to the joint capsule tissue.
 12. The method of claim 10,wherein the maintaining step comprises generally closing the jointcapsule over the prosthesis.
 13. The method of claim 10, wherein themaintaining step comprises suturing the prosthesis to the surroundingsoft tissue.
 14. The method of claim 10, further comprising the step of:conforming the shape of at least a portion of the prosthesis to at leasta portion of a facet of the facet joint.
 15. The method of claim 14,wherein the conforming step is performed after the inserting step. 16.The method of claim 14, wherein the conforming step is performed whilethe prosthesis is generally located between the facets of the facetjoint.